This application claims the benefit of a priority under 35 USC 119 to French Patent Application No. 0011520 filed Sep. 11, 2000, the entire contents of which are incorporated by reference.
The invention concerns the quality of a radiographic image of an object obtained by an X-ray apparatus having an antidiffusion grid. The invention is applicable advantageously but not exclusively to mammography examinations for the detection of microcalcifications inside a breast.
An X-ray apparatus, used notably in mammography, is equipped with an anti-diffusion grid placed between the object to be X-rayed, in this case a breast, and a receiver of radiographic images, for example, a CCD (charge-coupling) receiver. The antidiffusion grid is ordinarily composed of a series of strips which are all directed toward the focal point of radiation of X-rays emitted in the direction of the object and of the image receiver. Thus, the antidiffusion grids lets undiffused direct beams pass, while the diffused beams are absorbed by the strips. The resolution of the image receiver is generally finer than the space between two strips, which is typically in the order of 0.3 mm. As a result, the strips are visualized on the radiographic image obtained, which is particularly disturbing in mammography, for it renders the detection of microcalcifications more difficult.
One solution proposes displacing the grid during exposure, in rectilinear translation in its plane, that is, roughly perpendicular to the strips of the antidiffusion grid. The translation is carried out solely in one direction or alternately in both directions.
Another solution, as shown in FR-A-2,784,569, discloses a method of improvement of quality of an object obtained by an X-ray apparatus equipped with an antidiffusion grid with a law of displacement of the antidiffusion grid which is a continuous curve presenting a point symmetry relative to the point whose time coordinate is equal to half of the pickup time and whose spatial derivative of the time variable presents two symmetrical linear portions relative to the axis of symmetry passing through the middle of the range of displacement of the grid.
The invention is directed to substantially elimination of the visible traces of strips of the antidiffusion grid on the X-ray film.
The invention is also directed to obtaining an improvement of image quality with a mechanically simple solution for displacement of the antidiffusion grid.
The invention is directed to a particular profile of displacement of the antidiffusion grid.
The invention is also directed to an improvement of image quality realizing that at a beginning of exposure, the exposure time is known with a rather wide margin of imprecision, for example, on the order of 10%.
The invention is a method of improvement of quality of a radiographic image of an object obtained by an X-ray apparatus containing an antidiffuision grid, placed between the object and a receiver of radiographic images, a grid that is displaced in rectilinear translation in its plane on pickup of the image, between a starting position and an arrival position and according to a time displacement law with a time precision of approximately xc2x110%. The displacement law is a continuous curve presenting at least five separate parts, the displacement taking place at constant speed over at least two parts and at variable speed over at least one other part.
An embodiment of the invention also concerns a computer program comprising program code means for using the stages of the method, when the program is operating on a computer.
An embodiment of the invention also concerns a support capable of being read by a reading device of program code means which are stored there and fit for use of the stages of the method, when the program is operating on a computer.
An embodiment of the invention also concerns a radiological imaging device comprising an X-ray beam emitter, a receiver of the X-ray beam after it has crossed an organ to be studied, a moving antidiffusion grid and an arithmetical unit able to control the emitter, to control displacement of the antidiffusion grid and to process data coming from the receiver.